From 3913d1778318cd0c6bfb871148d38abb33ec7fd3 Mon Sep 17 00:00:00 2001 From: nasr Date: Wed, 28 Jan 2026 13:13:40 +0100 Subject: checkpoint --- xlib-tutorial/server.html | 89 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 89 insertions(+) create mode 100644 xlib-tutorial/server.html (limited to 'xlib-tutorial/server.html') diff --git a/xlib-tutorial/server.html b/xlib-tutorial/server.html new file mode 100644 index 0000000..a408834 --- /dev/null +++ b/xlib-tutorial/server.html @@ -0,0 +1,89 @@ + + +Xlib programming tutorial: What is all this "client-server" stuff ? + + + +

What does all this stuff about "client-server" mean ?

+ +Everybody says that X has a "client-server" architecture. So this must +be true, but what does it mean ? + +

+ +Well, basically a client-server architecture is conceptually a simple +thing, but the consequences may be a bit subtle, especially the way it +is implemented in the Xlib. + +

What is a client-server architecture ?

+ +A client-server architecture is a general mechanism for handling a +shared resource that several programs may want to access +simultaneously. In the case of X, the shared resources are the drawing +area and the input channel. If every process was allowed to write on +it at its will, several processes may want to draw at the same place, +resulting in an unpredictable chaos. Thus, only one process is allowed +to get access to the drawing area: the X server. The processes wanting +to draw stuff or get inputs send requests to the X servers (they are +"clients"). They do this over a communication channel. The X server +performs the requests for its clients, and sends them back replies. It +may also send messages without explicit client's requests to keep them +informed of what is going on. These messages sent by the server on its +own behalf are called "events". + +

Advantages of the client-server architecture

+ +The client-server architecture has several advantages, many of them +resulting from the ability to run the server and the clients on +separate machines. Here are some advantages: + +

A client-server architectured system can be very robust: since + the server runs in its own address space, it can protect itself + against poorly written clients. Thus, if a client has a bug, it + will crash alone, the server and the other clients still running + as if nothing has happened. + +
The client and the server don't have to run on the same machine, + so we have some communication mechanism here. + +
The client and the server may run on separate machines, resulting + in a better load distribution (possibly). + +
The client and the server don't have to run on the same hardware, + operating system, etc., giving a better interoperability. + +

+ +

Structure of the X client-server architecture

+ +As we already mentioned, the server and a client communicates over a +communication channel. This channel is composed of two layers: the +low-level one, which is responsible for carrying bytes in a reliable +way (that is with no loss nor duplication). This link may be among +others a named pipe in the Unix environment, a DECNet link and of +course a TCP/IP connection. + +

+ +The upper layer use the byte-transport channel to implement a +higher-level protocol: the X protocol. This protocol says how to tell +the server to request window creation, graphics drawing, and so on, +and how the server answers and sends events. The protocol itself is +separated into different parts: + +

How to connect and how to break a connection, +
how to represent the different data types, +
what are the requests and what they mean and +
what are the replies and what they mean. + +

+ +[to be continued]. + +

Christophe Tronche, ch.tronche@computer.org

+ + -- cgit v1.3